When Is It Appropriate For Arthrodiastasis Of The First MPJ?

By Peter M. Wilusz, DPM, and Guy R. Pupp, DPM

A Review Of Indications And Contraindications

   Indications for first MPJ arthrodiastasis include any joint with mild to moderate degenerative joint disease, with or without malalignment (transverse or sagittal plane) of the joint.    When it comes to severe degenerative joint disease, it may be beneficial to perform an arthrodesis or implant arthroplasty. However, one may still incorporate joint distraction when addressing joint malalignment issues via osteotomy correction.    Mild to moderate hallux abducto valgus with painful limitation of motion may also benefit from arthrodiastasis if one observes cartilage defects on preoperative testing/imaging or intraoperatively. Preoperative preparation of the patient is important when considering the use of external fixation for possible fixation of the osteotomy with distraction.    Contraindications for joint distraction include: ligamentous laxity (which may result in a more unstable joint); a severe loss of cartilage within the joint (end stage degenerative joint disease); vasospastic disorders and peripheral arterial disease; and active or sub-acute infections involving the joint. When it comes to joint distraction, proper evaluation and appropriate patient selection are essential for obtaining a predictable and satisfactory result.    Applying mini-external rail fixators is relatively simple but does require some experience. Ensuring proper placement of the transcutaneous pins is important in order to facilitate proper distraction as well as adequate and correct anatomic motion during the healing process. Inaccurate placement of pins will prevent movement about the first MPJ and cause mechanical abutment of the dorsal joint surfaces. Orienting the fixator in relationship to the joint to ensure motion is key to improving outcomes. The surgeon would usually perform and confirm all of these steps under fluoroscopy.    There are several manufacturers of small external fixators that one may use in joint distraction. In order to discuss the surgical technique, let us proceed to discuss proper mini-external fixator placement of the M-111 mini-rail (Orthofix, Inc.).

A Step-By-Step Approach To The Arthrodiastasis Procedure

   Prior to application and the appropriate osseous remodeling, one should perform joint debridement and subchondral drilling with standard closure. Be sure to inspect and mobilize the sesamoid apparatus for adhesions to the plantar aspect of the first metatarsal.    Insert a 2 mm Kirschner wire into the head of the first metatarsal from the medial side so it is in the center of the rotation of the joint. This point is slightly dorsal of the center point of an imaginary circle outlining the first metatarsal head. Orient the fixator so the body of the fixator with the distraction mechanism is facing the proximal phalanx. The hexagon at the center of the hinge should face outward.    Slide the articulating hinge over the Kirschner wire. Insert the 3 mm diameter bone screw through the distal seat of the distal clamp and insert the second screw into the proximal seat of the distal clamp. Manipulate the hallux, confirming that the movement is about the axis of the Kirschner wire. If not, remove and reset the Kirschner wire, adjusting the distraction mechanism as necessary.    After confirming motion about the axis of the first metatarsal, proceed to insert the 3 mm bone screws into the distal end of the first metatarsal.    Distract the joint 5 mm acutely (intraoperatively). Remove the Kirschner wire and tighten the articulated locking body screw. Be sure to lock the screw with the hallux in a neutral sagittal plane position.

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